The present invention relates to the field of polymer fiber extrusion processing and apparatus.
Conventional fiber forming methods and apparatus typically involves the extrusion of polymeric material through orifices. The rates, pressures and temperatures of the typical fiber extrusion process represent a compromise between economic requirements and the physical characteristics of the polymeric material. For example, the molecular weight of the polymeric material is directly tied to both melt viscosity and polymeric material performance. Unfortunately, improvements in polymeric material performance are conventionally tied to increased molecular weight and corresponding relatively high melt viscosities. The higher melt viscosities typically result in slower, less economically viable processes.
To address the high melt viscosities of higher molecular weight polymers, conventional processes may rely on relatively high temperature processing in an effort to lower the melt viscosity of the polymeric material. The process temperature may typically, however, be limited by degradation of the polymeric material at higher temperatures. In conjunction with increased process temperatures, the process pressures, i.e., the pressure at which the polymer is extruded, may also be increased to improve process speed. Process pressure may, however, be limited by the equipment employed to extrude the fibers. As a result, the processing speed in conventional processes is typically constrained by the factors discussed above.
In view of the issues discussed above, the conventional strategy in extruding molten polymer for fiber making is to reduce the molecular weight of the polymeric material to attain economically viable processing rates. The reduced molecular weight results in a corresponding compromise in material properties of the extruded polymeric fibers.
To at least partially address the compromises in material properties of conventional extruded fibers, the fiber strength may be improved by orienting the polymeric material in the fiber. Orientation is imparted by pulling or stretching the fiber after it exits the extrusion die. As a result, the polymeric material used for the fibers typically must have a substantial tensile stress carrying capability in the semi-molten state in which the polymeric material exits the die (or the fibers will merely break when pulled). Such properties are conventionally available in semi-crystalline polymers such as, e.g., polyethylene, polypropylene, polyesters, and polyamides. Thus, conventional fiber extrusion processes can be performed with only a limited number of polymeric materials.